Photographic processing equipment and processing chemicals continue to evolve to meet the increasing demand for convenient, low cost, and environmentally friendly photoprocessing. Some of the recent changes have included improved processing chemicals which provide faster processing for both film and paper, and smaller, more streamlined equipment which requires a reduced amount of photochemicals. One popular system is a minilab which is conveniently sized for typical production demands and which can conveniently process a roll of film and provide prints in a short time. In addition to processing consumer black and white film and paper, similar demands for convenience, low cost and environmentally friendly photoprocessing are needed for the processing of graphic arts films, aerial imaging products, microfilm, and medical imaging products (X-ray films).
However, even the advent of the minilab has not addressed all the needs and problems of modern photoprocessing. Two areas which particularly need addressing are 1) the increasing demand for photoprocessing capabilities in non-traditional photoprocessing environments and 2) the need to reduce the amount of replenishment necessary to keep a photoprocess system stable, both to decrease cost and to reduce the amount of effluent from processing machines. These two areas are often interrelated. In addition there is the never-ending desire to reduce processing time and/or the amount of chemicals needed to fully process various photographic materials.
The demand for non-traditional photoprocessing environments is also being fueled by the increase of digital image processing. As digital image processing becomes more prevalent, there is a growing need for hard copy from digital sources. Silver halide photographic hard copy can give the highest quality images, but is often found to be less convenient than electrophotographic or thermal technologies. Since the photographic processing of digital images would often be done in an office, home, or other non-traditional photoprocessing environments, the convenience of processing is of upmost importance.
Currently available processors can be inconvenient for home or office processing or for other small operations for the following reasons. First, the volume of the tank solutions that need to be prepared to fill a processor are still somewhat large for small-scale operations. Typical processor tank volumes of 10 to 25 liters for processor tanks require relatively large volumes of solutions to be handled.
Secondly, for low utilized systems, the processing solutions remain in the tank for a long residence time. The lack of `tank-turnovers` with fresh replenisher causes the solutions to evaporate and the components to oxidize, causing the chemical concentrations of the components to change. This leads to process control variability and precipitate or tar formation, both of which can affect sensitometry. Such low utilization problems are one of the largest obstacles for small-scale operations when using traditional processing equipment.
The need to reduce the amount of replenishment is driven by both cost and environmental concerns and is shared by large and small processors. This is especially difficult for disposal of waste for home, office or other small-scale operations. Photographic processors are equipped with replenisher solutions designed to maintain process activity at a steady-state, as sensitized goods are processed. The replenishers contain the necessary components to replace chemicals consumed or lost through oxidation or carryover in developing, fixing and washing and/or stabilization of sensitized materials.
In automated systems, as sensitized materials are processed, a signal is relayed to turn on the replenisher pumps, so that fresh solution is added to the process tanks. The rates that the solutions are added to the process are dependent on the concentration of components which can be attained in the replenisher solutions.
The replenishment rate in a processing system is set at the lowest rate possible. This reduces the effluent from the process, lowers handling of chemicals, reduces the amount of chemicals used, and reduces the energy needed to maintain operating temperatures. However, the amount replenishment can be reduced is dependent on the following factors.
1. Replenisher Stability--Once all components are combined into a single solution, the components begin reacting with each other and with oxygen, limiting the usefulness of the solution to the stability of the components. The usefulness of a mixed replenisher is normally 4-8 weeks, but may be as short as a few days. Solution stability may be enhanced by the use of covers which sit on top of the solution, eliminating air space which allows oxidation and evaporation. PA1 2. Concentrate Stability--Because of the reactivity of the various components with each other and with oxygen, it is necessary to separate the replenisher concentrates into two or more parts until they are to be used. Concentrates are normally stable for several years if properly stored. PA1 3. Productivity--The quantity of sensitized material processed daily is of concern, since low replenishment rates cause the tank solutions to be resident in the tanks for longer periods of time, subjecting them to oxidation, evaporation and interaction degradation. PA1 4. Carryover--Carryover is the solution carried over from one tank into the next with the sensitized materials. The lower the carryover, the more stable the solutions. When very little or no solution is carried over into the next tank, less dilution occurs and less replenisher is needed in the next tank and less chemical interaction degradation takes place. If the carryover is high, more solution is carried over and more replenisher is needed to compensate for dilution and chemical interaction degradation. If the carryover out of the tank is greater than the replenishment rate, the tank volume will decrease. This results in a loss in the process activity due to the resulting volume loss. This loss reduces the time the sensitized material is in the solution and could lead to processor malfunction. If tank volume is lost, processing solution must be added to maintain solution level. PA1 5. Evaporation-Oxidation--Evaporation and oxidation take place constantly with all processors. To control them, the area of solution exposed to the air needs be kept to a minimum. A surface which results in considerable evaporation and oxidation is the surface of rollers which are used to transport the sensitized material from one tank to another. Some processors have rollers which are partially submerged in the process solutions. The continual wetting and drying of these rollers increases evaporation and oxidation of the processing solutions. It is advantageous to have rollers either completely submerged or completely out of solution. Another way to reduce evaporation and oxidation is to reduce the flow of air over the solutions. PA1 6. Tank turnover--Tank turnover (TTO) is the time required to replace the process tank solution with fresh replenisher solution. Reducing the replenishment rate of solutions extends the residence time of the solutions in the processor, increasing the time per tank turnover. To reduce the time per TTO and replenishment rate, it is necessary to reduce the volume of the processor tanks or increase the utilization (productivity) of the processor. Reducing the volume of the tanks or increasing the utilization of the processor, will decrease the time per tank turnover and reduce the residence time of the solutions. The operator of the process may not be able to increase the utilization of the processor depending on the production demands. There is often a seasonal nature to the processor utilization with periods of low utilization occurring in production demand cycles. PA1 7. Precipitation/Crystallization--Components which are present in the tank solutions may increase in concentration due to seasoning (processing of sensitized materials) or because of evaporation. Because of their solubility, the components may precipitate or crystallize from solution, or form a tar-like phase separation. The increase of the level of certain components may cause the precipitation or crystallization or tar formation of other components by reducing their solubility. The lower the replenishment rate, the more likely that this will occur. PA1 8. Process by-product buildup--Materials washing out of the sensitized product, such as, sensitizing dyes, halides, calcium, silver, which accumulate in the solutions as they season out of the sensitized materials, or as they are formed from reactions during photoprocessing, may also precipitate, crystallize, or form tar-like deposits. This effect is more significant if an attempt is made to reuse or regenerate the waste solutions so that they can be used in the processor again. PA1 9. Pump accuracy--As the replenishment rates are reduced, the need for high accuracy, low-volume pumps becomes imperative. PA1 F is the flow rate of the solution through the nozzle in gallons per minute; and PA1 A is the cross-sectional area of the nozzle provided in square inches. PA1 ECD is the average equivalent circular diameter of the tabular grains in .mu.m and PA1 t is the average thickness in .mu.m of the tabular grains.
In particular, the amount of replenishment necessary is dependent on the level of utilization of the processor. When a traditional processing system has low utilization it cannot be operated using a low replenishment regime because the system is not stable.
The industry has attempted to compensate for low utilization problems and disposal problems by adjusting processing chemistry. For example, minilab film and paper processors run through a wide range of utilizations. One unit may experience a wide change of utilizations depending on the time of the year and production demands. A variety of processor chemical solutions can be made available to accommodate most situations by adding more preservative or to formulate for a higher replenishment rate.
Most minilab processors have been designed to operate "plumbless" (no water connections needed for washing of the prints or drains needed to dispose of effluents). To achieve a plumbless processor, it was necessary to design a wash system which allowed for the reduction of wash-water volume. This is accomplished with a stabilizer which stabilizes the solution, prevents processing by-products from being deposited on the prints or the tank walls, and incorporates a biocide to prevent biogrowth in solutions. The processors have been designed with countercurrent replenishment, with each tank of solution recirculated and heated.
However, all of the above options involve the need to purchase and use different processing solutions or make other accommodating actions for varying utilization conditions, a situation that can be inconvenient or confusing to the user. For example, the developer regenerators, while very effective at reducing effluent, involve additional equipment and operating steps which may be inconvenient for small-scale operations. Further, none of the above solutions are stable at very low utilization.
Current technology is reaching its limits with regard to size and processing capability. Problems of the small-scale operation such as low utilization, tank size, and processing cost cannot be fully addressed with alterations to existing equipment. Additionally, the ability to significantly reduce replenishment rates below current standards with existing equipment and chemistry no longer exists. Further, traditional systems have been maximized with regard to processing parameters. There is little flexibility left to reduce processing time or chemical consumption.